The present invention relates to a press die that is used for forming, for example, a separator for a fuel cell.
A typical separator for a fuel cell has a structure, for example, as shown in FIG. 7. The separator is formed of a plate 41 made of a hard material, such as titanium. The plate 41 has on its surface multiple grooves 42a at predetermined intervals. The plate 41 also has on its back grooves 42b, each of which is located between adjacent two of the above grooves 42a. The grooves 42a, 42b function as gas passages through which hydrogen gas and oxygen gas flow, respectively.
When forming such a separator for a fuel cell, a press die apparatus as shown in FIG. 8 is conventionally used, for example. The press die apparatus includes a lower die 43 and an upper die 44. The lower die 43 has on the upper surface a die surface 431 with grooves and protrusions, and the upper die 44 has on the lower surface a die surface 441 on which grooves and protrusions are formed to correspond to the die surface 431 of the lower die 43. The upper die 44 is arranged above the lower die 43 to be brought toward and away from the lower die 43. With a plate 41, which is a workpiece, placed on the die surface 431 of the lower die 43, the upper die 44 is brought toward the lower die 43 to press the plate 41 between the die surfaces 431, 441 of the dies 43, 44, so that the grooves 42a, 42b are formed on the plate 41.
When producing the lower die 43 and the upper die 44 of the press die apparatus, the surface of a die material is cut with a cutting tool to form the die surfaces 431, 441 having grooves and protrusions. In a case in which the die material is made of super hard metal, such as high-speed steel, the cutting tool easily becomes dull. Thus, it is difficult to form the die surfaces 431, 441 by cutting the die material at one stroke in a direction in which the grooves and protrusions extend on the die surfaces 431, 441 without replacing the cutting tool.
To deal with such a problem, a press die apparatus as illustrated in FIGS. 9 and 10 has conventionally been proposed. The press die apparatus has a lower die 43 formed by die blocks 45, which are separate rectangular columns. The die blocks 45 are placed on a base 46 and fitted in a frame 47 such that the die blocks 45 are aligned in the longitudinal direction and the transverse direction of the frame 47. A space member 48 is located between the inner surface of the frame 47 and each die block 45 adjacent thereto. According to this configuration, the die surface 431 with grooves and protrusions can be easily formed by cutting limited parts of the end faces of the die blocks 45 individually and then joining the cut surfaces of the die blocks 45. Although not illustrated, the upper die of the press die apparatus is configured by die blocks that are aligned as in the same manner as in the lower die 43.
On the other hand, Japanese Laid-Open Patent Publication No. 2008-296262 discloses a press machine of die-quench method, in which heated steel material is pressed by upper and lower dies. The lower die of the press machine is formed by separate die blocks, so that thermal expansion and contraction of the lower die as a whole are suppressed. The die blocks are arranged side by side on a base with clearances between the die blocks. In pressing operation, thermal expansion of the die blocks is absorbed by the clearances between the die blocks.